Fine Sediment Research Articles

Effects of Seasonal Variations in Seagrass Density and Storms on Sediment Retention and Connectivity Between Subtidal Flats and Intertidal Marsh

AbstractBoth submerged aquatic vegetation and salt marsh are important coastal ecosystems known for their effectiveness in sediment trapping and carbon burial. However, their proximity can lead to competition for limited sediment resources, potentially compromising their capacity to facilitate sufficient sediment deposition to withstand sea‐level rise. Here we applied the Delft3D flow and sediment transport model in a shallow coastal bay to assess how seasonal variations in seagrass density and storms modulate sediment retention and connectivity between subtidal flats and intertidal marsh. Results show that submerged seagrass meadows acted as temporary storage for fine sediment and altered the timing of sediment transport to an adjacent marsh through seasonal growth cycles. When seagrass occupied subtidal flats, sediment flux to the marsh was controlled by seasonal seagrass density variations, with peak fluxes during winter senescence. In contrast, wave‐induced sediment resuspension on the flats was the major contributor for marsh sediment input in the simulation with no seagrass, with peak storm‐driven fluxes in summer/autumn. Overall, seagrass meadows significantly increased annual sediment accumulation on the vegetated subtidal flats by tenfold, while reducing annual marsh sediment flux and edge erosion by 20%. Seagrass meadows and marsh were both able to maintain a sediment deposition rate comparable to the rapid sea‐level rise at the study site despite the absence of terrestrial sediment sources. Our findings highlight the strong seasonal control subtidal aquatic vegetation has in the vertical and horizontal dynamics of tidal flat‐marsh systems and provide insights that can inform wetland restoration and management strategies in similar systems.

Morphology and Sediment Dynamics of Blossom Shoals at Icy Cape, Alaska

AbstractCapes and cape‐associated shoals represent sites of convergent sediment transport, and can provide points of relative coastal stability, navigation hazards, and offshore sand resources. Shoal evolution is commonly impacted by the regional wave climate. In the Arctic, changing sea‐ice conditions are leading to (a) longer open‐water seasons when waves can contribute to sediment transport, and (b) an intensified wave climate (related to duration of open water and expanding fetch). At Blossom Shoals offshore of Icy Cape in the Chukchi Sea, these changes have led to a five‐fold increase in the amount of time that sand is mobile at a 31‐m water depth site between the period 1953–1989 and the period 1990–2022. Wave conditions conducive to sand transport are still limited to less than 2% of the year, however—and thus it is not surprising that the overall morphology of the shoals has changed little in 70 years, despite evidence of active sand transport in the form of 1‐m‐scale sand waves on the flanks of the shoals which heal ice keel scours formed during the winter. Suspended‐sediment transport is relatively weak due to limited sources of mud nearby, but can be observed in a net northeastward direction during the winter (driven by the Alaska Coastal Current under the ice) and in a southwestward direction during open‐water wind events. Longer open‐water seasons mean that annual net northeastward transport of fine sediment may weaken, with implications for the residence time of fine‐grained sediments and particle‐associated nutrients in the Chukchi Sea.

Promoting success in thin layer sediment placement: effects of sediment grain size and amendments on salt marsh plant growth and greenhouse gas exchange

Thin layer sediment placement (TLP) is used to build elevation in marshes, counteracting effects of subsidence and sea level rise. However, TLP success may vary due to plant stress associated with reductions in nutrient availability and hydrologic flushing or through the creation of acid sulfate soils. This study examined the influence of sediment grain size and soil amendments on plant growth, soil and porewater characteristics, and greenhouse gas exchange for three key U.S. salt marsh plants: Spartina alterniflora (synonym Sporobolus alterniflorus), Spartina patens (synonym Sporobolus pumilus), and Salicornia pacifica. We found that bioavailable nitrogen concentrations (measured as extractable NH4+‐N) and porewater pH and salinity were inversely related to grain size, while soil redox was more reducing in finer sediments. This suggests that utilizing finer sediments in TLP projects will result in a more reduced environment with higher nutrient availability, while larger grain sized sediments will be better flushed and oxygenated. We further found that grain size had a significant effect on vegetation biomass allocation and rates of gas exchange, although these effects were species‐specific. We found that soil amendments (biochar and compost) did not subsidize plant growth but were associated with increases in soil respiration and methane emissions. Biochar amendments were additionally ineffective in ameliorating acid sulfate conditions. This study uncovers complex interactions between sediment type and vegetation, emphasizing the limitations of soil amendments. The findings aid restoration project managers in making informed decisions regarding sediment type, target vegetation, and soil amendments for successful TLP projects.

Controls on terrigenous sediment supply to northwestern South China Sea based on a sediment trap record at Xisha Trough

The South China Sea (SCS) is the largest marginal sea in the western Pacific and comprises an ideal natural laboratory for studying deep-sea processes. Previous investigations in the region have primarily focused on surface currents and to a lesser extent on intermediate currents, while observations of bottom currents are scarce, hindering our understanding of deep ocean sediment transport and deposition mechanisms. Here, we carried out grain size measurement and end-member modelling analysis (EMMA) on samples collected by a sediment trap at a water depth of 1500 m in the Xisha Trough in the northwestern South China Sea. Grain size data shows that terrigenous material has particle sizes ranging from 0.3 μm to 745.9 μm and a peak at 4–11 μm. The EMMA result suggests that finer sediment accounting for an average of 48.2% of the sediment represents material transported by deep water currents (End-member 1; EM1), and this is primary sediment source in the region. Coarser sediment contributing to 32.9% of the sediment is the second most significant source (EM3), representing the deposits of surface currents influenced by monsoons and deposited close to the source. A third sediment type (EM2) constituting approximately 18.9% of the sediment exhibits a wide range of grain sizes and rapid changes, indicating transport in the bottom nepheloid layer triggered by anticyclonic eddies. Our study identifies three primary sediment transport mechanisms to the northwestern SCS, bridging present-day observations with paleoceanography and providing a crucial basis for future research on paleoceanographic reconstructions.

Organic Carbon Sources in Surface Sediments on the Northern South China Sea

AbstractThe burial of organic carbon (OC) in marine sediments regulates CO2 content in the atmosphere. However, the OC sources and their effect on the OC preservation in sediments of the continental marginal sea remain elusive. Here, we survey the abundance, stable carbon and radiocarbon isotopes of OC, as well as mineral surface area and grain size in surface sediments from the shelf to the abyssal plain of the South China Sea. We found that the marine OC comprises the 63 ± 9% and 78 ± 14% of sedimentary OC off South China and Luzon, respectively. The petrogenic OC contributing to sedimentary OC in these sites is generally higher than that of soil OC (22 ± 10% vs. 12 ± 6%). The sedimentary OC off Taiwan is predominantly derived from petrogenic OC, accounting for 57 ± 10%, with remaining consisting of marine OC (36 ± 10%) and soil OC (6 ± 1%). High soil OC contents are found in fine sediments on the inner shelf off South China, and high petrogenic OC contents occur in fine sediments off Taiwan. Marine OC contents are high in fine sediments on the middle shelf and upper slope off South China, but low in coarse sediments on the outer shelf and upper slope, and fine sediments on the lower slope and abyssal plain. The OC sources, mineral surface area, and oxygen exposure time of OC together control the preservation of OC in sediments with their relative importance differing on varying depositional settings of this sea.

Utilizing Fine Marine Sediment as a Partial Substitute for Sand in Self-Compacting Concrete Specially Designed for Application in Marine Environments

The disposal of marine sediments poses a significant economic and environmental challenge on a global scale. To address this issue and promote resource optimization within a circular-economy paradigm, this research investigates the viability of incorporating untreated fine marine sediments as a partial replacement for sand in self-compacting concrete (SCC) designed especially for application in marine environments (an exposure class of XS2 and a resistance class of C30/37 according to standard NF EN 206). The concretes mis-design incorporating 30% by weight of sediment as a sand substitute was initially designed with the modified Dreux–Gorisse method. The findings indicate that it is feasible to design an SCC suitable for marine environments, incorporating 30% sediment replacement content and without significantly compromising concrete properties, durability, or the estimated lifespan of the formulated concretes. The integration of marine sediment as a sand substitute into the SCC mix design reduces the amount of binder and limestone filler without compromising the paste volume. This results in a significant saving of natural sand resources and a reduction in CO2 emissions for SCC made with marine sediment.

System-scale dynamics of long-term sediment and phosphorus accumulation in contrasting valley-bottom wetlands in dryland landscapes of South Africa

Anthropogenic-induced acceleration of sediment and associated nutrients presents a serious challenge to water resource management across the globe. While wetlands are potential natural solutions, little is known of how well key wetland types attenuate downstream sediment fluxes and how these relate to local- and catchment-scale factors. This research aimed to develop an understanding of patterns and rates of sediment and phosphorus retention in valley-bottom wetlands in South Africa. The geomorphology, sedimentology and historical accretion rates of three wetlands which offered diversity in size, catchment position and degree of organic accumulation were compared to ascertain the impact of local- and catchment-scale factors. Estimates of sediment and associated phosphorus accumulation suggest higher rates in clastic sediment-dominated wetlands (1089–7655 g sediment m−2 yr−1, 0.4–1.6 g-P m−2 yr−1) compared to an organic sediment-dominated system (601–1308 g-sediment m−2 yr−1, 0.2–0.3 g-P m−2 yr−1). Sediment accretion rates generally increased longitudinally, indicating that distal wetland reaches act as sediment and phosphorus retention hotspots. Phosphorus distribution patterns were primarily attributed to variations in organic matter content and associated aluminium and iron complexing agents in fine-grained sediment deposits, while particle size distributions were less important. However, the relevance of individual complexing agents in phosphorus dynamics varied among wetlands with differing landscape conditions. Contrasts between these systems reflect variations in catchment lithology and hydroclimatic regime, which influence the relative magnitude of sediment supply and vegetation productivity. We postulate that intermediate-sized wetlands characterised by catchments around 900 ha in size, gentle longitudinal slopes (∼2 %), a high proportion of fine sediment deposition, limited organic matter breakdown, and a long vegetation growing season provide optimal conditions for sediment and phosphorus accumulation. This system-scale information is essential to guide management decisions to identify and prioritize within-catchment ‘hotspots’ of sediment and phosphorus retention.

Influence of Riparian Conditions on Physical Instream Habitats in Trout Streams in Southeastern Minnesota, USA

Rivers across the globe experience and respond to changes within the riparian corridor. Disturbance of the riparian corridor can affect warmwater, intermediate, and coldwater streams, which can negatively influence instream physical structure and biological communities. This study focused on assessing the influence of the riparian habitat on instream structure within the Whitewater River, a coldwater stream system within an agricultural watershed in southeastern Minnesota, USA. To understand the influence of the riparian zone on the physical instream habitat, twenty variables (riparian, n = 9; instream, n = 11) were measured at 57 sites across three forks of the Whitewater using a transect method every 10 m across a 150 m reach. We used a modified Wentworth scale approach to assess coarse and fine substrates to describe habitat conditions. Canonical correlation detected significant associations between riparian and instream variables across the river forks, and indicated that wider riparian buffers, more bank grass and shrubs, longer overhanging vegetation, limited bare soil, and more rocks on banks were significantly associated with increased instream cover, high levels of coarse substrates with reduced embeddedness, increased pool habitats, and reduced fine sediments. In contrast, excessive fine sediments, lack of riffle habitat, reduced coarse substrates, and high width to depth ratios indicative of an impaired instream habitat were associated with narrow riparian buffers and high percentages of bare soil on banks. Riparian corridors have the capacity to enhance and protect physical instream habitats and overall ecosystem health when managed properly. Wide, grassy riparian corridors with stable banks, overhanging vegetation, and limited shade from trees should protect and/or enhance the instream physical habitat, providing the structural diversity favored by aquatic communities. We recommend revising the current Best Management Practices to include monitoring for impairments in the riparia, while promoting and developing good land stewardship with private landowners which can be effective in improving river ecosystems in agricultural settings.

Phenotypic plasticity of a Baetid mayfly larvae (Baetis rhodani) at sites with high levels of deposited fine sediment

Abstract Excess fine sediment (particles <2 mm) delivery and deposition in freshwater systems is a significant factor in structuring aquatic communities and populations. Invertebrate gill surfaces can become covered with fine sediment, potentially compromising osmoregulatory function. Ionocytes are specialised structures for osmoregulation found on the tracheal gills of mayflies. The number of cells has been shown to change in order to maintain osmoregulatory demands under environmentally variable conditions. To investigate whether ionocytes vary in response to fine sediment pressure, individuals of Baetis rhodani were collected from two high and low fine sediment cover sites, respectively, in the UK. Tracheal gills were subsequently examined for the number of ionocytes present on the upper and lower gill surfaces, standardised by gill size. Results indicated that the number of ionocytes was significantly higher for mayflies collected from areas with high fine sediment cover. High fine sediment sites were also characterised by lower altitude and dissolved oxygen concentrations. Mayfly gills collected from high sediment cover sites were also significantly larger than those collected from low sediment sites. The results illustrate the potential for mayfly larvae to demonstrate phenotypic plasticity to the pressures associated with fine sediment but that these responses are likely dependent on the composition of fine sediment deposits (organic or mineral) and associated oxygen concentrations.

Modeling of multi-fractional suspended particle pathways in a shallow water basin under influence of strong winds

In this study, we investigate the complex dynamics of multi-fractional suspended particle transport in a shallow water basin subjected to strong wind conditions. Our research focuses on understanding the interplay between wind-induced advection and particle settlement, and its implications for sediment redistribution.Through our analysis, we reveal the distinct behaviors of different sediment fractions. Clay particles, constituting the lowest fraction in sediment cores, remain suspended throughout the simulation due to their low settlement velocity, with relatively stable concentrations. Conversely, the dominant fraction, medium silt, is suspended during intense wind events but quickly settles to the bed due to its higher settling velocity. Wind stress exceeding 0.05 Pa triggers particulate matter erosion, leading to its presence in the water column.Additionally, we explore the 2D distribution of sediment characteristics, including thickness, dry density, and mud fraction, to identify areas prone to erosion and deposition. Our findings demonstrate that coastal areas of the Taganrog Bay experienced significant erosion following strong wind events, exhibiting the thinnest sediment thickness and the highest dry bulk density. Deposition areas, characterized by thicker sediment layers and lower dry density, were often found in proximity to erosion zones, indicating the influence of particle resuspension and settlement processes.Furthermore, we analyze the implications of our findings on the vulnerability of specific regions to erosion and deposition. The central part of the sea contains moderately thicker sediment layers with a moderately high mud fraction, representing a zone of fine sediment accumulation. These fine sediments, including fine silt and clay, remain suspended for longer durations and are redistributed over greater distances by currents.Overall, our study provides valuable understanding into the multi-fractional suspended particle pathways and their interaction with strong winds in shallow water basins. The results contribute to a better understanding of sediment dynamics, which has implications for coastal management, environmental monitoring, and the preservation of benthic ecosystems.

Fine particle contents in sediment drive silica transport and deposition to the estuary in the turbid river basin

Changes in riverine sediment transport are an important part of land-sea geochemical cycling and further impact geochemical element fluxes in turbid rivers. However, as a vital nutrient element supporting primary productivity, silica mobilization from drainage in turbid rivers is overlooked. The turbid Yellow River has a strong ability to adsorb reactive silica, thereby exerting a substantial impact on the estuarine deposition of silica. Through an integration of monitoring databases, field sampling and historical hydrological data, we concluded that riverine fine particles control the exchangeable silica in the river and its estuary under soil erosion. Indoor simulation further revealed that the adsorbed content of exchangeable silica (ex-Si) in fine sediment constituted 35 % of total sediment matter. In addition, the transport of phosphorus and ex-Si was jointly regulated by fine sediment in global fluvial sediment transport, thereby exerting additional influence on the trophic structure of estuarine ecosystems. Against the backdrop of sediment budget deficit in the estuary, the heightened content of fine particles is depleting the silica storage from estuarine sediments.

A comparative analysis of missing data imputation techniques on sedimentation data

Sediment data pertains to various hydrological variables with complex sediment hydrodynamics such as sedimentation rates which are often incompletely presented. Thus, the availability of sedimentation data is of utmost necessity for data accessibility. A comparative analysis on the missing fine sediment data imputation performance was made based on four different techniques, namely the k-Nearest Neighbourhood (k-NN), Support Vector Regression (SVR), Multiple Regression (MR), and Artificial Neural Network (ANN), under the single imputation (SI) and multiple imputation (MI) regimes. Across different missing data proportions (10%-50%), the ANN demonstrated optimal results with consistent performance metrics recorded over both SI and MI regimes. For the highest missing data proportion (50%), the ANN presented the best imputation performance with a reported root mean squared error (RMSE) 0.000882, mean absolute error (MAE) 0.000595, coefficient of determination (R2) 71%, and Kling-Gupta Efficiency (KGE) 72%. The imputation performance ranking is as follows: ANN, SVR, MR, and k-NN.

Effect of initial pore water content and salinity on the resistivity of methane hydrate-bearing fine sediments

Methane hydrates are widely distributed in the soft silty-clayey soils of continental margin sediments. The resistivity method is generally used to detect their distribution state and monitor their kinetic reaction process. However, there are some major details to be elaborated on as to the occurrence state and the evolution of key characteristic parameters. Based on the kinetic reaction experiment under different lithological conditions (initial water content and pore water salinity), this research records the changing resistance of natural sand porous medium system during the cooling formation of hydrates by in-situ measurement. The Archie formula is further used to study the influencing factors of the resistance of hydrate-bearing sediments and how the resistance changes during hydrate formation. The results demonstrate that these two lithological parameters can significantly affect the resistivity of the hydrate-bearing natural sand porous media system. It is found that within a certain range, NaCl in pore water will inhibit the formation reaction of hydrates, while an increase of initial water content will enhance the hydrate production amount in the system. With the hydrate formation in the pores, the porosity and skeleton composition of the natural sand porous medium change as well, coupled with the salt-removing effect, which further changes the system resistivity. During hydrate formation, the system resistivity changes regularly in the cooling stage, hydrate nucleation stage, and hydrate formation stage. Our study systematically considers the influence of these geological parameters on resistivity characterization at different reaction stages during the formation of natural hydrates. Thus, it can serve as a technical reference for hydrate reservoir logging and other related issues.

Disentangling effects of multiple agricultural stressors on benthic and hyporheic nitrate uptake

Agricultural land use alters nitrate (NO3–) uptake dynamics in streams, but the specific mechanisms linking individual agricultural stressors to benthic and hyporheic uptake remain unclear. Using stream-side mesocosms and 15N-nitrate additions, we examined the individual and combined effects of fine sediment (FS) and augmented light and phosphorus levels (L&P) on benthic and hyporheic NO3– uptake rates. In absence of FS, L&P stimulated uptake of autotrophic and heterotrophic biofilms, leading to a 12- and 7-fold increase in the benthic and hyporheic compartments, respectively. Under ambient light and nutrient conditions, FS reduced by 3-fold benthic uptake, but effects were not significant. Conversely, in the hyporheic compartment, FS induced anoxic conditions, likely stimulating denitrification and causing a 14-fold increase in hyporheic uptake. When these stressors were combined, they did not interact in the benthic compartment. Conversely, in the hyporheic compartment they interacted antagonistically, with L&P diminishing the increase in uptake induced by FS. Our results indicate that the previously observed increase of whole-stream NO3– uptake in agricultural streams is attributable to nutrients and light stimulating benthic uptake, while fine sediment effects and the role of the hyporheic compartment to total uptake are modest. Moreover, the finding that stressor interactions vary with ecosystem compartments calls for a consideration of all compartments and their contribution to whole-system functioning in multiple stressor studies. We are beginning to understand how multiple interacting stressors affect stream functioning, but more mechanistic evidence is needed to disentangle whether additive or non-additive effects prevail in human-altered ecosystems.

Development of a leveling and loosening mechanism for fine sediments on a test track for planetary robots

Planetary robots must be extensively tested before they can be sent on a mission. Especially on loose soil, there is a need for tests with repeatable surface and soil properties to simulate the planetary use and to obtain reliable results for each test run. To achieve this, a leveling and loosening mechanism for a robotic test track is presented. By leveling and loosening in one motion, it enables easy and fast test preparation. Bio-inspired bear claws were designed and tested as loosening tools, which allow loosening with minimal resistance and a loosening effect of about 45%. The modular design allows the attachments to be easily interchanged to adapt the mechanism to different requirements or add additional functions like measurements of the soil properties. The paper provides details on the design and evaluation of the leveling and loosening mechanism.

Loess chronology and composition as interpreted through the lens of fossiliferous lake sediments in central Illinois, USA

Silty lacustrine and paludal records spanning from the penultimate deglaciation (late Illinois Episode) to the present are preserved in kettles formed during marine isotope stage (MIS) 6 that lie adjacent to the MIS 2 Manito terrace along the valleys of the Sangamon and Illinois Rivers. Geochemical, mineralogical, particle-size, and chronological records from two basins, Smith Lake and Lake Ben, provide a unique opportunity to assess loess age and provenance of the south-central Laurentide ice sheet. Here, I focused on deposits of redeposited loess of the last glaciation (Wisconsin Episode). Other than subtle laminations and fossils of emergent and aquatic plants and animals, the silty texture, chemical composition, and mineralogy of the lake sediment closely resemble Peoria Silt (loess). Sediment-core records sampled from Smith Lake and Lake Ben in Mason County, Illinois, confirm rapid deposition of proximal loess derived from the nearby outwash plain of the Illinois River from ca. 30.9−18.0 calibrated (cal) k.y. B.P. From 18.0−14.7 cal k.y. B.P., deposition of proximal loess was gradually replaced by far-traveled (distal) loess chiefly derived from Superior lobe provenance and global dust. The succession is capped by a cumulic gleysol that was truncated by recent plowing. Proximal loess deposits in lakes Smith and Ben are composed primarily of very fine sand, coarse silt, and medium silt (125−16 µm) compared to the distal facies (fine silt and finer sediment: <16 µm). Proximal loess that originated from outwash of the Lake Michigan lobe contains abundant Ca, Zr, Sr, illite, and magnetic minerals. The distal facies contains relatively abundant Rb, Al, K, Si, Cu, and Pb, and it is enriched in smectite (relative to illite) and depleted in magnetic minerals. Radiocarbon ages on terrestrial gastropod aragonite in loess from the nearby New Cottonwood School and Thomas Quarry sites indicate that Peoria Silt deposition ended between 18 cal k.y. B.P. and 16 cal k.y. B.P. At these localities, the upper part of the record is complicated by the modern soil, which has altered soil organic matter and leached carbonate. At Lake Ben, the radiocarbon record of emergent aquatic vegetation indicates that sediment accumulation rates and the ratio of proximal to distal loess decreased at the correlative interval that yielded the youngest snail shell ages at Cottonwood School. The upward increase in element concentrations such as Al and decrease in coarse/fine silt ratios in the modern soil are prominent features in the Lake Ben record dating from 18−14 cal k.y. B.P. This correlation strongly suggests that many of the features of the modern soil were not developed into uniform parent material but, rather, were inherited from incremental addition of distal loess to proximal loess, collectively identified as Peoria Silt. The paucity of key elements (Cd, Hg, Se, Ag, Au) in this transition zone suggests limited contributions from western lobes (i.e., Des Moines and James lobes), but abundant Ti and Cu suggest a contribution from the Superior lobe. A new wrinkle in this interpretation is that the rise in elements such as Al, Rb, and Si suggests significant additions from generic dust from unknown sources.

Evaluating the impacts of SRC willows on phosphorus export from a temperate grassland micro-catchment

Willows (Salix SPP.) are increasingly being grown as a source of biomass which can be harnessed for energy production at a commercial scale as one example of a Short Rotation Coppice (SRC) crop. What is less widely understood is the role of the plants in reducing nutrient loads when planted as a nature-based solution to mitigate diffuse pollution from agricultural lands. Strategically planted woodland and forest can play a major role in Nature Based Solutions (NBS) approaches. SRC willows were planted in a 22-ha grassland micro-catchment located on a research farm in Northern Ireland, which is regularly grazed by cattle and sheep. The micro-catchment comprises a small ditch with upstream and downstream monitoring points where a pair of autosamplers were used to collect water samples for nutrient analysis. It was possible to reconstruct a timeseries of hourly discharge in the ungauged micro-catchment using the SHETRAN hydrological model. Subsequently, the modelled flows were used to estimate daily phosphorus (P) loads at both upstream and downstream monitoring points from the measured P concentrations. The nearly four years (June 2018–April 2022) of monitoring data allowed P loads to be calculated for pre-planting, juvenile trees and mature trees phases. A baseline scenario was run without any changes to the model; this evaluated the changes in P loads from the catchment. A further Post-Willows scenario “P–W” modified some model parameters and evapotranspiration to represent the land use change due to the willow plantation. The results from the baseline were evaluated and showed that (i) there was a statistically significant reduction in particulate P (PP) and total P (TP) concentrations at the outlet of the micro-catchment; (ii) a statistically significant reduction in PP and TP loads, indicating that the willows were reducing PP export (losses) probably by trapping fine sediment in the ditch. Results from the P–W scenario showed a smaller than expected decrease in discharge from the model results. The overall export of TP from the micro-catchment could be further decreased by additional planting of SRC willows, but the export of soluble forms of P did not decrease by a significant amount post-planting which is a recommendation for further study in mitigation programmes. The use of SRC willows in riparian buffer strips (RBS) which are a common form of NBS, has shown promising results in terms of trapping particulate forms of P. The layout of the RBS should also be carefully designed in terms of maximising the buffer strip width, here the areas planted was optimised to make best use of unproductive farmland. If the RBS can be designed to maximise the interception of runoff flowing downhill from agricultural fields then the removal rate should be even higher.

Формации каменноугольно-нижнепермских карбонатных отложений бассейна верхней Печоры (Северный Урал)

The Upper Pechora basin is part of the northeastrn margin of the European Platform. In the Paleozoic, it was located within the carbonate shelf of the passive continental margin. According to A. I. Eliseev, Visean terrrigenous-carbonate (platamovy type) and Upper Visean-Lower Artinskian carbonate (kaleydovy type) formations occupy the upper part of the final sedimentation cycle of the formations row. According to new data, the history of the geological development of the Upper Pechora basin of the Late Visean-Asselian period has significant differences. Four types can be distinguished in the structure of sediments according to the composition of rocks: siliceous-clay-limestone, limestone, dolomite-limestone, siliceous-limestone. They were formed during three stages respective to the time of formation of three transgressive-regressive cyclites: the Visean-Serpukhovian, Bashkirian-Moscovian, Upper Carboniferous-Lower Permian. The studied deposits are divided into lithological complexes: siliceous-clay-carbonate of open sea (Tulian), siliceous-carbonate of open sea (Aleksinian-Early Mikhailovian, Bashkirian-Early Moscovian, Kasimovian-Midle Gzhelian), carbonate of shallow-shallow (Late Mikhailovian-Protvinian, Moscovian), and also the Late Gzhelian-Asselian shallow-depression (siliceous-limestone, limestone, clay-limestone). Lithological complexes, formed in open-sea conditions, belong to formations from the platamovy type and in shallow-shallow conditions — to formations from the kaleidovy type (by Eliseev, 2008).

Aggradation and reworking of an alluvial fan in response to climate changes on the south bank of Lake Qinghai, NE Tibetan Plateau

Alluvial fans in the piedmont zones of mountains respond most rapidly to tectonic activity, base-level conditions, and climate changes. These allogenic signals are effectively recorded by the external morphology and internal sedimentary characteristics of the fan. Based on field survey interpretation and integrated optically stimulated luminescence (OSL) chronology, we selected a case study of the modern Xiangpi Fan on the south bank of Lake Qinghai, NE Tibetan Plateau, and built a three-stage alluvial fan pattern since Marine isotope stages 3 (MIS3), namely, the debris flow lobe building stage (DFLBS), aeolian building stage (ABS), and streamflow reworking stage (SRS). The climatic indicators, such as the total organic carbon (TOC) flux, precipitation, and sediment particle size flux, are highly correlated with the above stages, indicating that the sedimentary process and changes in fan morphology effectively record orbital climate changes in the Lake Qinghai basin. During the DFLBS, the cold-dry climate accelerated the sediment yield sufficiently, leading to many coarse-grained sediments and low TOC flux being imported into the basin through debris flow processes. During the ABS, the extreme dry-cold climate caused the stagnation of fan development, and aeolian processes dominated the transport of fine sediment. In the SRS, warm-humid conditions led to limited sediment yield and perennial stream power, which promoted the transport of fine-grained material and TOC to the basin by braided–meandering channels. This study provides an excellent case showing how an alluvial fan responds to climate oscillations through changes in sedimentology and geomorphology.

Integrated modelling of flow-sediment transport and power generation in the Three Gorges Reservoir

Reservoirs play a crucial role in regulating runoff and generating energy. However, they also lead to significant sedimentation in the reservoir area. In this study, we propose an integrated model that combines a 1-D hydro- and sediment dynamic module with a power generation module. The model considers both suspended and bed load transports. This model is applied to the Three Gorges Reservoir (TGR) and evaluate its performance against corresponding measurements. The results demonstrate that:① the proposed model accurately reproduces the processes of flow and sediment transport, bed deformation, and power generation during the hydrological years of 2019 and 2020. The relative errors for average discharge and bed deformation volume are <6 % and 10 %, respectively. Moreover, the calculated total power (982 × 108–1115 × 108 kW·h) closely agree with the measured values (969 × 108–1118 × 108 kW·h); ② the inflows of small tributaries have a noticeable impact on the calculated water discharge in the TGR. This impact will lead to a 16 % increase in average discharge and alter the magnitudes and occurrence times of flood peaks; ③ the flocculation of fine sediment particles significantly affects sediment transport, particularly in the sub-reach close to the dam. This flocculation will result in a 37 %–57 % reduction in average suspended sediment discharge and a 63 %–93 % reduction in peak sediment discharge. This research provides a comprehensive tool for simulating flow and sediment transport as well as power generation, which can support the optimal regulation of the TGR.